https://bugzilla.redhat.com/show_bug.cgi?id=1096269
--- Comment #7 from Matthew Heon mheon@redhat.com --- I've identified the root cause of this. Docker uses a buffer to store incoming signals before sending them to the (https://github.com/dotcloud/docker/blob/master/api/client/commands.go#L538). This buffer is, in current versions of Docker, size 1 - multiple signals arriving near-simultaneously will overwrite one another. I've submitted a pull request to increase the size of the buffer (https://github.com/dotcloud/docker/pull/6508).